Project Summary Young adults (ages 18 to 25) compared to other age groups, have the highest rate of cannabis use disorder (CUD) (SAMHSA, 2018) and are the least likely to seek CUD treatment (Kerridge et al., 2017). Recent advances in digitally delivered treatments show promise for this population. Beyond the cost-effectiveness of digital treatments compared to traditional therapies, an advantage is the perception of increased privacy, which can lessen stigmatization for young adults (Hoch et al., 2016). Young adults interact with approximately 128 texts per day (Burke, 2016), supporting this treatment modality. The association between youth social context and exposure, uptake, and continuation of cannabis use is strongly established in the literature. A large national study of young adults in substance use treatment found strong and persistent effects of peers on cannabis use, where increases in peer substance use worsened treatment outcomes (Davis et al., 2016). Beyond peer effects, environmental effects, such has neighborhood disorder have been shown to be an important and potent influence on cannabis use (Mason et al., 2017).Young adults interact with peers grounded in meaningful places, shaping their health behavior trajectories, underscoring the interactive nature of place and peers (Mason, 2010). Despite this evidence of peers and place influences on cannabis use, there has been little research on the integration of social and environmental components within cannabis interventions. Peer Network Counseling-txt (PNC-txt) explicitly targets the peer and environmental context and can be delivered via personalized, automated text messages. PNC-txt is a substance use intervention that focuses on place-based peer relations as a mechanism for behavioral change. PNC-txt's hypothesized active ingredient is ?peer network health,? which is the sum of risk and protective behaviors of a young adult's close peer network. PNC-txt delivers 112 automated, personalized texts over 4 weeks, as well as booster messages delivered PRN. Key responses from participant's baseline assessment automatically populate the content of each participant's tailored intervention. PNC-txt is ideally suited for young adults comfortable with this technology. Our specific aims are: Aim 1. Test the efficacy of PNC-txt on cannabis use cessation with 1000 young adults with Cannabis Use Disorder. Sub-Aim 1. Test the cost-effectiveness and scalability of PNC-txt in two large state universities. Aim 2. Test the extent to which the direct effect of PNC- txt is mediated by participants' peer network health, which in turn is moderated by participants' gender. Aim 3. Test whether PNC-txt reduces the effect of stress, craving, and activity space exposure to high-risk cannabis use environments on cannabis use over time.